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    <title>Document</title>
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    <script>
      function fn1(a) {
        console.log("fn1");
        return function (b) {
          console.log("fn2");
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        return function (c) {
          console.log("fn3");
        };
        return a + b + c;
      }
      //在第一次return ，就中断了函数，运行结果fn1 fn2
      var res = fn1(1)(2)(3);
      console.log(res);
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